Find the expected reward in an expectimax-based dice rolling game?
If I understand,

With probability $p$ the robot select no re-roll (action $D$).
With probability $1-p$ the human uniformly select an action between $A,B,C,D$.

Thus the expected reward for if the robot helps is
$$R_{AH}= p\cdot D+(1-p)\frac{A+B+C+D}{4} = \frac{(A+B+C)(1-p)+D+3pD}{4}$$